Position reproducing mechanism



July 30, 1946. J, D Em 2,405,066

- POSITION REPRODUCING MECHANISM Filed March 28, 1942 2 Sheets$heet lINVENTOR JAMES D.TEAR

BY If)? ATTORNEY 3%, 194-5 .3, 5; TEAR POSITION REPRODUCING MECHANISMFiled March 28, 1942 2 Sheets-Sheet 2 INVENTOR JA M Es D. TEARllllllllllflllllllll'l I I] Z0214 ,a/QM/I- 1-! TT ORNE Y Patented July30, 1946 UNITED STATES PATENT OFFICE POSITION REPRODUCING lJIECHANISMApplication March 28, 1942, Serial No. 436,685

9 Claims. 1

The invention relates to mechanisms for reproducing position andparticularly to such mechanisms of the follow-up type in which thetransmission system operates a control member for a power unit termed aservo-motor.

The invention is applicable with self synchronous transmissions in whichthe torque of the receivers is zero when they are in synchronism withtheir transmitters, and which employ dual transmissions of differentspeed ratios, the units of positional value transmitted by the low speedtransmitters being relatively large or coarse, and those transmitted bythe high speed transmitters being relatively small or fine.

A characteristic of embodiments of the invention is the fact that thereis but a single control member for the amplifying power unit, and thatthis control member is operated by a drive which is selectivelycontrolled by the fine and coarse receivers dependin upon the positionalerror, that is, the extent to which the driving or motion receivingmember fails to synchronize or agree in position with the original ormotion transmitting member; and it is with the proper transfer andmaintenance of this selective control that the invention is moreespecially concerned.

In such follow-up systems the power unit operates reversely upon thecontrol member to shut.

oiT the power when the transmitted movement is completely reproduced.The movement of the control member is usually limited in both directionsand a relief connection or yieldable coupling in the drive from areceiver to the control member frees the receiver rotor from limitationin synchronizing with its transmitter. The construction of this reliefconnection is such that the drive for the control member is biased to apositional relation with the receiver rotor and is self synchronous orself-correcting within the range of a limited error beyond which ittends to increase the error in order to return to biased relation, byreturning in the wrong direction.

In accordance with this invention an auxiliary power unit arranged underthe control of the coarse receiver is connected to supplement the driveto the control member and to cause the coarse receiver to assume chargeof the control member for the servo-motor as long as the error exceedsthe limited amount. The auxiliary power unit may be an electric motorthe energizing circuit of which includes a pair of contacts one of whichis moved with the coarse receiver and the other of which is moved in thesame path by the drive for the servo-motor control member operated bythe fine receiver, and at the same re.-

tio of movement thereto that the coarse receiver bears to the finereceiver. The two contacts are spaced a predetermined distance when therelief connection is in its biased position, and the distance isdecreased in proportion as the relief connection departs from its biasedposition until the contacts engage whereupon the auxiliary motor isenergized and assumes control of the control member. This occurs beforethe condition is reached where the relief connection would jump to afalse position and thus throw the control member further out of phaserelation with the fine receiver rotor.

The invention also contemplates suitable clutching means in theconnection with the auxiliary motor which is engaged only When thecoarse receiver is in charge and thus relieves the fine receiver of theload of the armature so long as the fine receiver is in charge.

This invention is adapted for actuating a servo-motor control of thetype in which the velocity at which the power driven response approachesthe velocity of the transmitted movement, such as a signal, is limitedto some function of the discrepancy between the received signal and thepower driven response. Such a type of control is desirable whensynchronizing the response with the signal as in starting up the systemor whenever the response may depart from the signal for any reason, suchas a shift of the receivers to a difierent pair of transmitters.

Other objects and advantages of the invention will appear from thefollowing description of the embodiment of the invention shown in theaccompanying drawings.

Fig. 1 shows diagrammatically an embodiment of the invention used inconnection with a simple form of servo-motor control.

Fig. 2 shows a modified form of servo-motor control in which theservo-motor is controlled so that the velocity at which the error inresponse is removed is a function of the error.

The two speed transmission shown is of the type disclosed for example inthe patent to Hewlett and Willard No. 1,559,524. The two transmitters land 2 are geared together by gearing 3 such that motion applied by amotion transmitting member 4 will move the rotor of transmitter l at ahigh speed relative to that of the rotor of transmitter 2, say 36:1. Therotors of the receivers 5 and 6 will have the same ratio of movement.

The rotor of the fine receiver 5 is connected by a shaft 1 to one sideof a centralized relief connection or yieldable drive coupling 8 theother 3 side of which i connected by shaft 9, bevel gears in and shaftii to one side of a control differential l2. Specifically the coupling 3is of the construction shown in the patent to Poitras and Tear N0.2,13%,488.

A reversible power motor l3, shown as an electric motor, is connected byshaft it, bevel gears 55 and shaft it to a second side of controldifferent al l2, the shaft l4 also being connected to drive the loadwhich it i desired to position in accordance with the transmittedpositional value. The third member of differential l2 actuates adirectional control member H, in this case a movable electric contact,which is energized by'a source of power it and is alternativelyconnected to the motor l3 by the leads of reversing contacts iii and 2s.The motor is is connected to the other side of the power source it by alead 2|.

It will be understood that as the rotor of the receiver motor 5 isturned in response to the transmitted value, the contact ll will bemoved to close one or the other of the motor circuits and the powermotor will rotate in a direction to position the load in accordance withthe movement of the motion transmitting member, and at the same time themovement of shaft it will be transmitted to the differential it throughthe shaft i6 and neutralize the input to the differential, therebyopening the contact ll and stopping the motor 63.

The shaft 22 of coarse receiver 6 is connected through a yieldablecoupling 23, similar to coupling 8, to rotate an insulated contact 2" onthe end of radial arm 25. The contact 2 3 cooperates with two insulatedcontacts 26 and El located on opposite sides of the contact 24 andcarried by the arm 23 which i mounted for rotation coaxially with thearm .25. The arm 28 i directly connected to and is rotated by a gear 29which is driven through reduction gearing 3%] by a gear 3! on shaft 9.The ratio of the gearing '33 is the same as that of the gearingfl, andhence the rotation of the arm 28 relative to the shaft 9 is the same asthe ratio of rotation of the coarse transmitter unit relative to that ofthe fine transmitter unit.

The shaft 9 carries a gear 32 which i geared with one member 33 of aclutch unit 34. The other member 35 of the clutch unit is rotatablyconnected to the armature of a reversible electric motor 36 by gears 3iand shaft 38 on which the member 35 is slidably mounted. The clutchmember 33 is freely mounted on shaft 33 but is restrained against axialmovement. Surrounding shaft 3% is a stationary coil 39 and a field frameii) of magnetic material. The clutch member 35 and shaft are also ofmagnetic material and therefore when the coil 39 is energized the memberwill be pulled into engagement with a friction surface, such as cork, onthe member 33. Thus rotation of motor 35 will be communicated throughthe clutch unit 3 5 to the shaft i3.

Three slip ring ll, 62 and 63 on the shaft of arm 23 are electricallyconnected respectively with the center contact 24 driven by coarsereceiver t, and the two contacts 26 and 2'! driven by the shaft 9.Brushe contacting these slip rings connect with the windings of motor 36through leads 55 and it respectively. The common lead 416 includes asource of power All and the coil 39 in series relation. It is apparent,therefore, that as the contact 2 touches either of contacts 23 and 2?the energizin circuit of motor 36 is closed to produce a torque in onedirection or the other, and at the same time clutch 4 34 is engaged, andthat the torque of motor 36 is applied on shaft 9.

The operation will be apparent from the foregoing description. Theyieldable drive couplings have on one side a cam and on the other aspring pressed follower, the cam surface tapering in both directionsfrom a high spot to a diametrically opposite low spot The spring causesthe follower to seek the low spot. If the two sides get out of angularagreement so far that the cam rides over the high spot the spring willreturn the follower to the low spot by a continuation of movement in thesame direction and thus further increase the error. In other words thedrive is self correctin only up to substantially of error.

It is this fact that determines the spacing of the contacts 26 and 27.The arms 25 and 23 are so set that the contact 24 is midway betweencontacts 26 and 27 when the couplings are in their biased position. Letit be assumed that power motor i3 lags in its following and hence thatthe input of shaft I i into the differential I2 is not-counteractedsufiiciently fast by the input of shaft [6. The contact ill will berotated against either contact id or 2b and as the error accumulates thecam follower of coupling 8 will ride up the cam surface against thespring tension. Arm 28 similarly lags but in the reduced ratio, and thespacing of contacts 26 and 21 is so determined that the appropriate oneis engaged by the contact 24 just before the cam follower reachesthehig'h spot of the cam and hence before the coupling 8 can jump ahead.The motor 36 is thereby energized, and the clutch being at the same timeclosed, the motor torque is applied to the shaft 9 in a direction toprevent the shaft from jumping ahead if the error increases and thefollower passe over the high spot, and thus from increasing the effectof the error.

Assuming the ratio of 36:1, one complete rotation of the fine receiveror 360 of movement of the member l represents one-thirty-sixth of acomplete rotation of the coarse receiver, or 10 of movement of the arm25. If the follow-up is accurate the contacts 2% and 2'! will move alongin synchronism with the contact 24 and keep it centralized. However asthe follow-up gets'out of synchronism the coupling 8 begins to yield andthe drive of arm 28 gets correspondingly out of step but at the reducedratio. When the shaft fl is 180 out of phase with the shaft 1, the arm28 i 5 out of phase with the arm 25. The maximum spacing of the contact23 and 21 is such that just before that condition is reached the contact24 engages, but, of course, the spacing may be less.

Conditions arise in use, particularly at the start of the operation,When the disparity between the positions of the motion transmitting andreceiving members will greatly exceed the range within which the systemis self correcting and which require perhaps one or more complete turnsof the fine receiver and a partial turn of the coarse receiver to be fedinto the control differential to bring the follower'member intopositional agreement with the transmitter member. It will be seen thatalthough both the coarse and fine receivers are turning over, the coarsereceiver is in controlof the input to the differential l2, until thecontacts 24, 26 and 21 are satisfied and open the circuit of the motor36, but when the torque of this auxiliary motorbecomes zero the shafttreturns to'control of the fine receiver and the follow-up motor isthereby sensitively controlled to bring the follower member into exactsynchronism, when the contacts I1, [9 and 20 are satisfied and thecircuit of the motor 13 is opened.

In the servo-motor control shown in Fig. 2 the contacts I9 and 20 aremounted on an arm 48 extending from a shaft 49 mounted in axialalignment with the shaft on which the contact I? is mounted. The shaft49 carries a pinion 55 meshing with a gear on a shaft 52, The shaft 52has secured to it an arm 53 to the end of which centralizing springs 54are attached. The shaft 49 also carries a gear 55 which-meshes with apinion 56 connected to drive a drag disc 57. The drag disc is shown asrunning in a chamber 58 filled with a liquid such as oil, but any formof drag device may be employed. The gear 55 carries a pin 59 adapted toengage a fixed pin 60 and thereby limit the rotation of gear 55 and arm48 carrying the contacts [9 and 20.

With this form of servo-motor control the centralizing springs 54 willmaintain the contacts l9 and in a fixed position during normaloperation, that is, when the response represented by shaft [6 remainssynchronized with the signal represented by shaft II. If for any reasonthe response, represented by shaft It, does not agree with the signalrepresented by shaft II, the contact I! will displace the contacts [9and 29 against the centralizing effect of the springs 54. Thisdisplacement may correspond to several turns of the fine receiver motor5 and is only limited by the stop pins 59 and 60. It will be seen thatthe receiver motor 5 will remain in direct control of the drive 9 eventhough the response may differ from the signal by an amount representedby several turns of receiver 5. It will also be seen that the contact 24will remain centered between the contacts and 21 during the accumulationof this difference.

When the stop pins 59 and 60 come into contact and stop the movement ofcontacts is and 29, contact I! is also stopped and shaft 9 is forcedfrom its biased position relative to receiver 5 until contact 24 engageseither contact 26 or 2"! and the motor comes into action as explained inconnection with Fig. 1.

When contacts l9 and 29 are thus displaced from their central positionthe centralizing force resulting from the springs 54 is substantiallyproportional to the displacement. As the response from motor l3 causescontact I! to move from its engaging contact the springs 54 will movethe engaging contact toward the central position. This motion will beopposed by the drag disc 51 so that the rate at which the contactsreturn to their central position is proportional to their displacement.The motor I3 can therefore remove the error only at the rate at whichthe contacts return to their central position. During the return of thecontacts l9 and 25 to their central position the shaft carrying contactI! is limited to the same rate. This shaft represents the error betweenthe response from servomotor i 3 and the receiver 5 and therefore theerror can only be removed at a rate which is determined as a function ofthe displacement, that is, of the error.

This speed control in attaining synchronism is the subject matter of mycopending application Serial No. 432,237.

It is obvious that the principle exemplified in the illustratedembodiments of the invention may be otherwise applied without departingfrom the scope of the invention as defined in the follow ing claims.

I claim:

- 1. A position reproducing mechanism comprising coarse and finereceivers of a self synchronous transmission system having apredetermined ratio of relative movement, a servo-motor, an enersizingcircuit for the servo-motor including a movable contact, operating meansfor the movable contact having a yieldable drive connection with andbiased to a definite angular relation to the fine receiver, a responseconnection from the servo-motor operative to neutralize the effect ofthe operating means upon the movable contact. a pair of movablecontactable elements one coupled to be driven by the coarse receiver andthe other coupled to be driven in the same direction by the contactoperating means at the said predetermined ratio of movement thereto, thesaid elements being positioned a definite distance out of contact whenthe contact operating means is in its biased relation to the finereceiver, and means actuated by the engagement of the contactableelements for supplementing the bias of the operating means.

2. A position reproducing mechanism comprising coarse and fine receiversof a self synchronous transmission system having a predetermined ratioof relative movement, a servo-motor, an energizing circuit for theservo-motor including a movable contact, operating means for the movablecontact, drive means yieldably connecting the contact operating meansand the fine receiver and including a cam and a spring pressed followerbiasing the parts to a definite angular relation and operative toreverse the angular direction of bias when a limited departure frombiased relation is exceeded, a response connection from the servo-motoroperative to neutralize the effect of the operating means upon themovable contact. a pair of movable contactable elements one coupled tobe driven by the coarse receiver and the other coupled to be driven inthe same direction by the contact operating means at the saidpredetermined ratio of movement thereto, the said elements beingpositioned a definite distance out of contact when the contact operatingmeans is in its biased relation to the fine receiver, and means actuatedby the engagement of the contactable elements for applying a predominantbias to the operating means to prevent reversal.

3. A position reproducing mechanism comprising coarse and fine receiversof a self synchronous transmission system having a predetermined ratioof relative movement, a servo-motor, energizing means for theservo-motor including a movable control member, operating meansincluding a relief cam operatively connecting the rotor of the finereceiver with the control member, response means operated by theservo-motor for neutralizing the action of the fine receiver rotor uponthe control member, a pair of contacts movable in a common path, onecoupled to be driven by the coarse receiver and the other coupled to bedriven in the same direction by the control member operating means atthe said predetermined ratio of movement thereto, the said pair ofcontacts being spaced a definite distance when the fine receiver rotorand the control member operating means are in synchronism, the reliefcam permittingdeparture from synchronism sufi'iciently to allow the pairof contacts to engage, an auxiliary motor, an energizing circuit for theauxiliary motor including the pair of contacts, and means operativelyconnecting the auxiliary motor to m ns the control member operating.

4:. A position reproducing mechanism comprising coarse and finereceivers of a self synchronous transmission system having apredetermined ratio of relative movement, a servo-motor, energizingmeans for the servo-motor including a movable control member, operatingmeans including a relief cam operatively connecting the rotor of thefine receiver with the control member, response means operated by theservo-motor ior neutralizing :le action of the fine receiver rotor uponthe control member, a pair of contacts movable in a common path, onecoupled to be driven by the coarse receiver and the other coupled to bedriven in the same direction by the control member operating means atthe said pre determined ratio of movement thereto, the said pair ofcontacts being spaced a definite distance when the fine receiver rotorand the control member operating means are in synchronism, the reliefcam permitting departure from synchronism sufficiently to allow the pairof contacts to engage, an auxiliary motor, an energizing circuit for theauxiliary motor including the pair of: contacts, means operativelyconnecting the au:: iliary motor to the control member operating means,a normally open clutch in the said connecting means, and meanscontrolled by the said pair of contacts for closing the clutch,

5. A position reproducing mechanism comprising coarse and fine receiversof a self synchronous transmission system having a predetermined ratioof relative movement, a' servo-motor, energizing means for theservo-motor including a movable control member, operating means for thecontrol member, a relief drive connecting the control member operatingmeans and the rotor of the fine receiver and including a cam and aspring pressed follower biasing the said operating means and rotor to adefinite angular relationship at which the movable control mem her issynchronized with the said rotor and yieldable to permit departure fromsynchronism, response means operated by the servo-r o'tor forneutralizing the action of the fine receiver rotor upon the controlmember, a pair of contacts movable in a common path, one coupled to bedriv by the coarse receiver and the other coupled to be driven in thesame direction by the control member operating means at the saidpredetermined ratio of movement thereto, the said pair of contacts beingspaced a definite distance W11 .3. the fine receiver rotor and thecontrol mern 1 operating means are in synchronism, where the contactsmay engage as the yieldable p permit departure from synchronism, anauxil motor, an energizing circuit for the an iary r tor including thepair of contacts, and m operatively connecting the auxiliary motor tothe contact operating means.

6. A position reproducing mechanism comprising coarse and fine receiversof a self-synchronous transmission system having a prede termined ratioof relative movement, a servo motor, energizing means for theservo-motor including a movable control member, operating means for themovable control member having a yieldable drive connection with andbiased to a definite angular relation to the fine receiver and having aresponse connection from the servomotor, a pair of relatively movablecontrol elements coupled to be relatively moved by the coarse receiverand the control member operating means at the said predetermined ratioof relative movement, and means actuated by the pair of control elementsfor supplementing the 8 bias of the operating means when the relativemovement of the control elements exceeds a predetermined amount.

7. A position reproducing mechanism comprising coarse and fine receiverof a self synchronous transmission system having a predetermined ratioof relative movement, a servomotor, energizing means for the servo-motorincluding two relatively movable, cooperative control members, operatingmeans for one of the movable control members having a yieldable driveconnection with and biased to a definite angular relation to the finereceiver, a response connection from the servo-motor to the said movablecontrol member, the second movable control member being adjustablymounted, means biasing the adjustable control member toward a positionto efiect positional agreement between the operating means and theservo-motor, means to retard the return movement of the biased memberfrom a displaced position, the control members coacting to displace theadjustable member an amount proportional to the error in positionalagreement between the operating means and the servo-motor, a pair ofrelatively movable control elements coupled to be relatively moved bythe coarse receiver and the control member operating means at the saidpredetermined ratio of relative movement, and means actuated by the pairof control elements for supplementing the bias of the operating meanswhen the relative movement of the control elements exceeds apredetermined amount.

8. A position reproducing mechanism comprising coarse and fine receiversof a self synchronous transmission system having a predetermined ratioof relative movement, a servo motor, means for energizing theservo-motor including primary and secondary contacts, operating meanshaving a yieldable drive connection with and biased to a definiteangular relation to the fine receiver, a response connection from theservo-motor coacting with the operating means to position the primarycontact, a pair of movable contactable elements one coupled to be drivenby the coarse receiver and the other coupled to be driven in the samedirection by the operating means at the said predetermined ratio ofmovement thereto, the said elements being positioned a definite distanceout of contact when the operating means is in its biased relation to thefine receiver, means actuated by the engagement of the contactableelements for supplementing the bias of the operating means, thesecondary contact being yieldably biased to open contact relation to theprimary contact when the operating means and the response connection arein positional agreement, the two contacts coacting to effect adisplacement of the secondary contact an amount proportional to an errorin said positional agreement, and means to retard the return of thesecondary contact to the biased position when displaced therefrom.

9. A position reproducing mechanism comprising coarse and fine receiversof a self synchronous transmission system having a predetermined ratioof relative movement, control operating means having a yieldable driveconnection with and biased to a definite angular relation to the finereceiver, a, pair of relatively movable control elements coupled to berelatively moved by the coarse receiver and the control operating meansat the said predetermined ratio of relative movement, means actuated bythe pair of control element for supplementing the bias of the controloperating means when the relative movement of the control elementsexceeds a predetermined amount, a servo-motor operably connected todrive a response shaft, means difierentially connecting the controloperating means and the response shaft to actuate a control for theservo-motor to bring the response shaft into angular agreement with thecontrol 10 operating means, and means associated with the control forthe servo-motor effective to cause the servo-motor to bring the responseshaft into angular agreement with the control operating means at a ratewhich is a function of the lack of angular agreement of the responseshaft with the control operating means.

JAMES D. TEAR.

